a) Field of the Invention
The present invention relates to a method of manufacturing a field emission type element, and more particularly to a manufacture method for a field emission type element which emits electrons from a tip of a field emission cathode.
b) Description of the Related Art
A field emission type element emits electrons from a tip of a sharp emitter (field emission cathode) by utilizing electric field concentration. For example, a flat panel display is made of a field emission emitter array (FEA) having a number of emitters disposed in a predetermined pattern. Each emitter controls the luminance and the like of each pixel of the display.
A manufacture method for a field emission type emitter has been proposed, which forms a film of independent-dispersive ultra-fine particles on a sacrificial film (insulating film) on a concave shape mold.
A report on a field emission element utilizing a B-W film appears in "Field Emission Element Utilizing B-W Film" by Akama, et al, the Japan Society of Applied Physics, Spring, 1995, preliminary reports No. 2, p. 640, 30p-T-3.
JP-A-5-211030 discloses a field emission element whose cathode is made of electron emitting material filled in holes of an aluminum porous anodized oxide film.
FIG. 4B is a cross sectional view illustrating a process of forming an emitter electrode made of ultra-fine particles having an average diameter of 10 nm or smaller, according to conventional techniques (see U.S. patent application Ser. No. 09/017,865, filed on Feb. 3, 1998, now U.S. Pat. No. 5,981,305 which is incorporated herein by reference). A substrate 60 has a gate electrode 61 formed thereon and an insulating film 62 formed on the gate electrode 61. An inner spacer 63 is formed on an inner wall of a hole formed through the insulating film 62. A hole having the same cross section as the bottom of the inner spacer 63 is formed through the gate electrode 61. A sacrificial film 64 of Si oxide is formed over the whole surfaces of the inner spacer 63 and insulating film 62 and on the surface of the substrate 60 exposed at the bottom of the gate hole. As an emitter electrode, conductive and independent-dispersive ultra-fine particles 65 were coated on the sacrificial film 64 and baked. Although baking for 5 minutes at 150.degree. C. provided a good embedding performance for ultra-fine particles, baking for 5 minutes at 200.degree. C. generated a small void in a ultra-fine particle group 65. Baking for 5 minutes at 300.degree. C. generated a large void (vacant hole) 66 which broken the tip portion of the emitter electrode 65 and disabled a voltage to be applied to the emitter tip.
Generation of a void results from a growth and volumetric shrinkage of fine particles, and may be ascribed to poor wettability to the surface of the Si oxide film 64. It is desired to lower the baking temperature as low as possible in order to prevent an increase in the diameters of the voids and fine particles. In order to lower the emitter resistance, baking is required to be executed at about 250.degree. C. If the emitter resistance is large, an electric field intensity at the emitter tip becomes weak because of a large voltage drop, so that electrons are emitted less or not emitted. Even if a voltage applied across the emitter and gate electrodes is raised, a driver circuit becomes expensive and complicated and a power consumption increases.
Independent-dispersive ultra-fine particles of Au or Ag have poor adhesion to glass and SiO.sub.2. In order to prevent peel-off of a mold or support substrate during manufacture processes which peel-off is caused by poor adhesion to the mold or support substrate and by a difference of thermal expansion coefficient between materials, it is necessary to avoid a high temperature process.
A field emission element utilizing a B-W film has different heights of the gate and emitter electrodes so that an electric field at the tip of the emitter electrode becomes weak.
A field emission element having the cathode made of electron emitting material filled in holes of an aluminum porous anodized oxide film cannot be formed through self-alignment. Namely, it is necessary to design it by taking into consideration a lateral position misalignment of the gate and emitter electrodes. Therefore, a space between the gate and emitter electrodes broadens, which means that the electric field at the emitter tip weakens.
The electric field characteristics and electron emission characteristics vary with the position relation and distance between the emitter and gate electrodes. Manufacture of a field emission element with the controllable size and position of an emitter electrode tip is an important factor to obtaining a desired element performance.